Study the reaction between human alpha 1-proteinase inhibitor and elastase including the rate of formation and disintegration of uni-unimolecular complex, as affected by temperature, and enzyme to inhibitor ratio. Attempt to determine linear structure of the reactive region of human alpha 1-proteinase inhibitor. Exclude possible effects of proteinases likely to contaminate elastase. Prepare sufficient amounts of bovine pancreatic secretory isoinhibitors of purity required for X-ray diffraction study. Inhibitor from swine colostrum. Utilize newly established separation of acidic (high molecular weight) inhibitor from the basic (low molecular weight) inhibitors, and separate the latter into isoinhibitors (presumably two) without using trichloroacetic acid, and thus preserving sialic acid in the inhibitors. Characterize the high molecular weight inhibitors in terms of similarity to blood plasma alpha 1-proteinase inhibitor.